1. Field of the Invention
This invention relates to drop-on-demand ink jet printheads and more particularly, to a thermal ink jet printhead having an integral silicon filter over its ink inlet and process for fabricating the printhead with such filter. A copending, commonly assigned application Ser. No. 624,390, filed Nov. 30, 1990, entitled "Ink Jet Printhead Having Integral Filter" to Campanelli et al. discloses a related invention.
2. Description of the Prior Art
A typical thermally actuated drop-on-demand ink jet printing system uses thermal energy pulses to produce vapor bubbles in an ink-filled channel that expels droplets from the channel orifices of the printing system's printhead. Such printheads have one or more ink-filled channels communicating at one end with a relatively small ink supply chamber and having an orifice at the opposite end, also referred to as the nozzle. A thermal energy generator, usually a resistor, is located in the channels near the nozzle at a predetermined distance upstream therefrom. The resistors are individually addressed with a current pulse to momentarily vaporize the ink and form a bubble which expels an ink droplet. A meniscus is formed at each nozzle under a slight negative pressure to prevent ink from weeping therefrom.
U.S. Pat. No. 4,589,952 to Behringer et al discloses a method of making trenches having substantially vertical sidewalls in a silicon substrate using a three-level mask comprising a thick photoresist layer, a silicon nitrite layer, and a thin photoresist layer. Openings are formed in the thin photoresist layer and silicon nitrite layer by reactive ion etching in CF.sub.4. The openings are continued through the thick photoresist by etching in an atmosphere containing oxygen. The exposed surface of the silicon substrate is then etched in a CF.sub.4 atmosphere containing a low concentration of fluorine. Also disclosed is a method of making an electron beam transmissive mask wherein the openings are made using a three level mask and reactive ion etching of silicon using the etching technique of this invention.
U.S. Pat. No. 4,417,946 to Bohlen et al discloses a mask for structuring surface areas and a method of manufacture of such mask. The mask includes at least one metal layer with apertures which define the mask pattern and a semiconductive substrate for carrying the metal layer. A semiconductor substrate has through holes that correspond to the mask pattern. The through holes in the semiconductor substrate extend from the metal covered surface on the front to at least one tub shaped recess which extends from the other back surface into the semiconductor substrate. Holes are provided in a surface layer in the semiconductor substrate. The surface layer differs in its doping from the rest of the substrate and the holes which are provided in the surface layer have lateral dimensions larger than the apertures in the metal layer so that the metal layer protrudes over the surface layer.
U.S. Pat. No. 4,639,748 to Drake et al discloses an ink jet printhead having an internal filtering system and fabricating process therefor. Each printhead is composed of two parts aligned and bonded together. One part contains a linear array of heating elements and addressing electrodes on one surface. The other part has a parallel array of elongated recesses for use as ink channels and a common ink supplying reservoir recess in communication with the ink channels. The reservoir recess contains an integral closed wall defining a chamber with an ink-fill hole. Small passageways are formed in the internal chamber walls to permit passage of ink therefrom into the reservoir. Each of the passageways have smaller cross-sectional flow areas than the nozzles to filter the ink, while the total cross-sectional flow area of the passageways is larger than the total cross-sectional flow areas of the nozzles.
U.S. Pat. No. 4,864,329 to Kneezel et al discloses a thermal ink jet printhead having a flat filter placed over the inlet thereof by a fabrication process which laminates a wafer-size filter to the aligned and bonded wafers containing a plurality of printheads. The individual printheads are obtained by a sectioning operation, which cuts through the two or more bonded wafers and the filter. The filter may be a woven mesh screen or preferably an electroformed screen with predetermined pore size. Since the filter covers one entire side of the printhead, a relatively large contact area prevents delamination and enables convenient leak-free sealing.
U.S. Pat. No. 4,169,008 to Kurth discloses a process for producing uniform nozzle orifices for an ink jet printhead, wherein holes are anisotropically etched through a silicon wafer. To overcome the effect of variation in thickness of the wafer on the through holes, the wafer is masked on both sides, photopatterned and deeply etched on its reverse side, then etched on its obverse side to create uniformly sized nozzles therein.
U.S. Pat. No. 4,106,976 to Chiou et al discloses a method of manufacturing an ink jet nozzle for a printhead, wherein a silicon wafer is masked on both sides with an inorganic membrane or layer such as silicon dioxide, silicon nitride, glassy materials and the like. The mask on the reverse side is patterned, and anisotropically etched to produce through holes therein which expose the membrane mask on the obverse side. The membrane mask on the obverse side is patterned and precisely etched to form nozzles. This also overcomes the effect of etched nozzle sizes caused by variation in wafer thickness.
U.S. Pat. No. 4,455,192 to Tamai discloses a method of manufacturing a multi-nozzle ink jet printhead wherein a single crystal silicon substrate or plate is masked and an etch stop layer is implanted therein and a second single crystal silicon substrate is then grown onto the first over the patterned etch stop layer. The second silicon substrate is masked and anisotropically etched, so that a through recess is formed in the second substrate exposing the etch stop and the first substrate is through etched in areas without the etch stop to form nozzles therein.
U.S. Pat. No. 4,733,823 to Waggenener et al discloses the use of an etch stop layer of diffused phosphorous in the obverse surface of a silicon substrate and then coating both surfaces with an etch resistant material. The etch resistant material on the reverse side is patterned and anisotropically etched to produce recesses having the etch stop layer as a relative thin floor. The etch stop layer is patterned to form nozzles therein.
One problem associated with thermal ink jet technology is the sensitivity of ink droplet directionality to particulates in the ink. Print quality is directly related to accurate placement of the ink droplets on a recording medium and droplet directionality determines the accuracy of the ink droplet placement. It has been demonstrated that higher print quality is achieved with particulate-free ink sources and the degree of particulate-free ink is related to how close the final filtration of the ink is to the ink jet printhead. One source of particulate contamination is the manufacturing environment itself. At least partial solution to particulate-induced misdirectionality problems is to construct the entire transducer structure in a clean environment. However, complete particle-free fabricating environments are not economically practical. This invention reduces the problems of particle contamination during the fabrication of an ink jet printhead, as well as providing an ink filtration means during printing by the printhead.